One-way, flap-type pressure relief valves are commonly used in applications such as vehicle ventilation systems. Typically, they serve to relieve the over-pressure that may occur within a nearly air-tight passenger compartment of a vehicle when, for example, a door of the vehicle is rapidly closed, while preventing the entry of air from outside the vehicle into the passenger compartment. Valves used for this purpose generally comprise a frame or housing which is mounted to an aperture formed in a panel enclosing the passenger compartment and defines an air passageway through the panel. The valve has one or more internal valve seats over which a plurality of valve flaps lie. The flaps comprise relatively thin, flexible members and overlie the valve seats on the exterior side of the passenger compartment. Each flap is fixed to the housing along one peripheral edge. When an over-pressure condition occurs within the passenger compartment, the flaps move away from the valve seats, bending or hinging adjacent their fixed edge to allow air to flow through the air passageway out of the passenger compartment. When the air pressure has equalized on both sides of a valve or when the pressure on the exterior becomes greater, the flaps swing or bend back to engage the valve seats and block airflow into the passenger compartment.
Valves of this general type are often manufactured by injection molding the housing and the valve flaps as separate pieces and then joining the two components by any one of several different methods. U.S. Pat. No. 5,601,117 teaches that holes formed along an edge of the flap are placed over pins projecting from the corresponding portion of the housing. The ends of the pins are then flattened to form a locking cap which secures the flap over the peg. U.S. Pat. No. 5,419,739 discloses a valve flap in the form of a flexible sheet having integrally formed tabs which are forced through respective slots formed in the housing. U.S. Pat. No. 5,194,038 discloses a valve wherein the flaps are connected to the housing by molding the flaps in situ integrally with the housing, but of a different, more flexible material than that of the housing. The flap is molded such that it is engaged along one edge with a slot formed in the housing. Each of these various methods of construction has inherent disadvantages, generally related to the fact that producing the valve as separate components that must be assembled is complex, time consuming, and/or labor intensive, adding to the overall cost of the finished component.
United Kingdom Patent Application 2,298,917A discloses a valve wherein the housing and the flaps are injection molded simultaneously and in the same mold from a rigid plastic material, and a more flexible plastic is subsequently over-molded onto the housing and the flap along one edge thereof to connect the two components and form a hinge which allows swinging movement of the flap. But because of practical limitations inherent in the injection molding process, specifically the problem known as "die lock," the housing cannot be molded in a single piece in its completed configuration. Instead, wall portions of the housing against which the flaps are to seal in the completed part must be molded outside of the housing, then inserted into their operative positions inside of the housing after the over-molding has connected the flaps to the housing. These additional steps add to the complexity and cost of manufacturing the valve.
Accordingly, there is a need for a simpler, more easily manufactured design for such pressure relief valves.